1. Field of Invention
The present invention relates to a variable compression ratio apparatus, and more particularly to a variable compression ratio apparatus for providing improved dynamic stability of dual link type eccentric links and dual link type swing links.
2. Description of Related Art
In general, the thermal efficiency of a heat engine is increased as a compression ratio is increased. In a spark-ignition engine, the thermal efficiency thereof is increased by advancing ignition timing up to a predetermined level.
However, in the spark-ignition engine, abnormal combustion may occur when advancing the ignition timing in a state of a high compression ratio, and this may cause damage to the engine. Therefore, there is a limitation in advancing the ignition timing, thereby resulting in the deterioration in output power.
A variable compression ratio (VCR) apparatus is an apparatus which changes a compression ratio of an air-fuel mixture in accordance with an operation state of the engine.
The variable compression ratio apparatus raises the compression ratio of an air-fuel mixture when the engine is driven at a low load in order to improve fuel economy. Further, the variable compression ratio apparatus lowers the compression ratio of an air-fuel mixture when the engine is driven at a high load in order to prevent knocking and to improve output power of the engine.
U.S. Pat. No. 6,581,552 teaches a variable compression ratio apparatus in the related art. In the variable compression ratio apparatus, a connecting rod is connected to a piston defining a combustion chamber, the connecting rod is connected to a crankshaft, and an eccentric ring is coupled to a portion where the connecting rod is connected to the piston.
An eccentric swing member is connected to the eccentric ring, the eccentric swing member is connected to a slide by means of a coupling, and the slide is connected to a driving device so that the slide is moved by the driving device.
In the variable compression ratio apparatus, the slide is moved by operation of the driving device, and the motion of the slide is transferred to the eccentric swing member via the coupling so that the eccentric swing member is rotated. The rotational motion of the eccentric swing member changes a height of a top dead center of the piston via the connecting rod, thereby changing the compression ratio of the combustion chamber defined by the piston.
Such a variable compression ratio apparatus requires a rigid structure, a stable operation and a simplified structure with respect to the eccentric swing member.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.